1. Field of the Invention
This invention relates to a method for dicing semiconductor substrates by which the wafer of substrate containing mesa semiconductor elements is separated into a plurality of pellets.
2. Description of the Related Art
Known methods for dividing a semiconductor substrate having mesa semiconductor elements into a plurality of pellets are chemical cutting and blade dicing techniques. The chemical cutting technique is to perform chemical dicing by etching as disclosed in U.S. Pat. No. 4,383,886. On the other hand, the blade dicing technique is to carry out mechanical dicing by means of blade dicers or the like. The latter method proceeds as follows: first, a semiconductor substrate is attached to a flat plate, such as a glass plate, using wax as adhesive; secondly, after the semiconductor substrate has been diced with a blade dicer, the wax is removed; and finally, damaged layers created during blade dicing are etched away by a mixed acid, such as a combination of hydrofluoric acid and nitric acid, to produce separated pellets.
However, such chemical cutting and blade dicing techniques have the following drawbacks. The chemical dicing technique takes a long time to finish dicing since etching is normally performed on one-side surface only. Moreover, the etching also develops in the lateral direction, so that to produce as large a pellet as that obtained by the blade dicing technique, it is necessary to increase the size of pellet by the amount of loss due to the lateral etching. In other words, the number of chips divided from a single wafer is declined. Contrarily, the blade dicing technique per forms dicing in a shorter time and with a smaller loss, but it is not best suited for the dicing of a semiconductor substrate in which mesa semiconductor elements are formed. This is because the uneven surfaces of a semiconductor substrate having mesa semiconductor elements makes it difficult to hold the substrate in place through vacuum absorption and necessitates attaching it to a glass plate or the like as mentioned above. It is troublesome to attach a semiconductor substrate having uneven surfaces to a flat plate without generating air bubbles. The existence of air bubbles may permit small size pellets to come off during dicing, resulting in a reduction in the yield.
As noted above, for substrates containing mesa semiconductor elements, conventional dicing methods cause a large pellet loss due to unwanted lateral etching and a reduced yield because of the difficulty in supporting a semiconductor substrate.